Exposure control apparatus



y 7,1935. A. B. FULLER 2,000,589

EXPOSURE CONTROL AI PARATUS Filed Aug. 10, 1931 I gwuento'o:

W/ZMQ/Q 0 m X @m an mq Patented May 7, 1935 mm. EXPOSUREOONTBOLARAIATUS Albertlhller,llochester,N.Y.,ndmrto- Eastman Kodak corporation oi New York Rochester, N.:Y., a

Applicaflon bllgllst 10.1931, Serial No. 556,199 3 Claim. (c1. ass-41.5)

My invention relates to automatic light timing devices particularly adapted for use in photographic printing where a range of unvaryin'g exposures is required.

One object or my invention is to provide a practical and reliable control circuit which will automatically vary the period of exposure in accordance with variations in the intensity of the light source due to any cause in such a way as to give a definite ultimate amount 01' light for a given exposure.

Another object of my invention is to provide exposure controlling mechanisms which will selectively give diii'erent required exposures. Another object is to provide a control circuit having a plurality of settings which may be used one at a time. Another object is to provide an exposure controlling mechanism having variable light integrating means for automatically obtaining a range of predeterminede Other objects will appear from the following description and the novel features will be pointed out in the appended claims.

Figure 1 of the accompa y drawing shows a circuit organization whereby my invention may be carried into eiiect and Figure 2 shows a modified light integrating system.

A light source i adapted to be energized from a source of power 2 through a switch 8 furnishes light to a printing plane 4 for exposing asensitive emulsion in any well known manner. A photo-electric element 5' positioned to be illuminated by the source I is connected in shunt relation with a condenser i.

The condenser 6 is adapted to be charged by abatterylthroughacontactlandtobedischarged through the photo-electric element I. The capacity in circuit with the cell 5 may be selectively varied by switching in one or more of the condensers 9, II, and II. The switch I is normally open and may be closed by momentarily closing a hand operated contact I! which connectsthe coil llot-theswitchithrougha normally closed contact It to the source of power lat the same time opening switch I. Acriticalrelay llotthegase'ous dischargetype having its grid and anode connected to the condenser 8 and its anode and cathode connected to the source I through theoperating coil I! of the contact I controls the opening or the switch 3.

. Inthe operation of the device the capacity in circuit with the condenser O is set at a value whichisknowntogivethedesiredexposureat the plane 4. The switch I being open the contact I is closed and the condenser is. charged to the potential of the battery I. The contact I! is momentarily closed which energizes the coil l3 and closes the switch The closing of the switch 3 completes the circuit of the coil II which holds the switch 3 closed until the circuit is opened by the contact ll. The closing of the switch I also energizes the light source I to start the exposure and opens the contact I in the battery circuit. The condenser 8 now discharges through the element 5, the conductivity of which corresponds to the intensity or the light received from the source I. The potential oi the grid of the relay decreases with the potential 01' the condenser as it discharges, and when the potential reaches the critical value, a

t H between the anode and the cathode which energizes the coil l6 and opens the contact It.

The opening of the contact ll breaks the circult through the coil It and permits the switch 3 to open to discontinue the exposure and to remove the anode voltage for stoppin the cursource I. The push button It controls the oltheswitchttoenergizethelight 'and the critical relay I 5 controls the I closes to energize the t l completes the-cir- I through the element I and g The rate at which the pothe condenser I depends conductance oi the element I and through a photoconductive element to integrate light is described in detail in United States application Serial No. 536,061, filed May 8, 1931, by Armand Georges Denis.

I may use any well known type of critical relay and probably the simplest would be a grid glow tube which operates as readily with A. C.

' lents of my invention will readily suggest themselves to persons skilled in the art without departing from the scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. The combination with an electric circuit, a photographic lamp in said circuit, a switch for making and breaking said circuit, a light sensitive element the conductivity of which varies with the intensity of said lamp, 0. capacity in series with a battery and said element, means for closing the battery circuit when said lamp is energized and means controlled by the charge on said capacity for opening the lamp circuit, said capacity being selectively variable.

2. A control circuit for a photographic lamp including a switch for making and breaking the lamp circuit, a photo-sensitive element positioned to be illuminated by said lamp, a condenser and a battery, means for simultaneously making said circuit and for connecting said element and said condenser in series relation with said battery whereby said condenser is charged through said element and means for breaking said circuit when said condenser has charged to a pre-determined potential.

3. An exposure controlling mechanism adapted to selectively give a variety of pre-determined exposures including electric storage means oi adjustable capacity and a photo-sensitive element, an electric lamp, 8. switch for closing a circuit to said lamp, means for charging said storage means through said element and means for opening the circuit of said lamp in response to a predetermined charge on said condenser, the conductance of said element being determined by the intensity of said lamp.

ALBERT B. FULLER. 

